Borat was a lot more clever than this article gives it credit for. As Cohen pointed out in an interview, every single scene had to end a specific way for it to move the plot along as required, so Cohen had to provoke the correct responses from those who appeared in the film. So he did write the screenplay, just with unknowing participants.

You missed the weirdest of all: the Best Documentary Feature win for THE HELLSTROM CHRONICLE, a David L. Wolper production in which fictitious entomologist “Dr. Nils Hellstrom” explains, in overheated verbiage, that it will not be long before insects put their superior social organization to work on eliminating mankind and taking over as masters of the planet. It was obvious even from the credits that there was no “Dr. Hellstrom,” so the Academy apparently felt that the excellent microphotography made up for the fact that the entire framing device was a not-particularly-convincing hoax.